Refining of fatty oils



June 10, 1958 Filed Oct. 12, 1954 Oll A. v. AYRES ETAL REFINING OF FATTYOILS 2 Sheets-Sheet 2 Soup Stock Heater Mixed Oil and Reagent REFININGon FATTY OILS Arthur U. Ayres, Philadelphia, and Frederick Smith,Huntingdon, Valley, Pa., assiguors to The Sharples Corporation, acorporation of Delaware Application October 12, 1954, Serial No. 461,86314 Claims. (Cl. 260-425) invention pertains still more particularly to'the refining of fatty oils withsodium carbonate.

Fatty oils are ordinarily refined by adding to the oil an aqueousalkaline solution, followed by conditioning or other treatment, and thenby separating from the oil the soapstock formed. The purpose of suchrefining is to neutralize and remove the free fatty acids present, toremove whatever gums may be present, to remove impurities and/or toimprove oil color.

Sodium carbonate which is commonly known as soda ash is a desirablereagent for the alkaline refining of fatty oils, since theoretically atleast it will not saponify neutral oil in a refining process, and isavailable in large amounts at low cost.

In the neutralization of fatty acids by means of sodium carbonate,considerable quantities of gaseous carbon dioxide are evolved, thereaction being illustrated by equations as follows: r v

wherein R is a hydrocarbon radical having for example between 11 and 17carbon atoms. This formationof carbon dioxide and its presence in thereaction'mixture has heretofore been considered to present considerabledifficulties in the refining. In, any event it has been found impossibleto carry the foregoing illustrated neutralization of fatty acids toanywhere near approaching completion when employing a stoichiometricequivalent of sodium carbonate based on free fatty acids, with theresult that the amount of sodium carbonate necessary to neutralize thefree fatty acids is very considerably in excess of the theoreticalstoichiometric quantity, i. e., when considering both sodium ions of.sodium carbonate available for neutralization purposes.

. A .process known in the trade as the soda ash process is'in largescale commercial use, and involves the addition of an aqueous solution ofsodium carbonate to the oil in substantial excess. The. resultingmixture cannot be satisfactorily separated under ordinary conditions,since carbon dioxide is evolved in such volume as to interfere with theseparation of the soapstock from the oil, In this commercial processthis difficulty, is overcome by introducing the mixture into a flashchamber while at an elevated temperature and "subjecting it to a vacuumtherein. The carbon dioxide and the major portion of the water presentare thereby removed from the mixture. After the carbon dioxide andwater'have been removed, the resulting dehydrated; mixture'is rehydratedby admixing therewith additional aqueous United States Patent 2,838,553Patented June 10, 1958 5-5 sodium carbonate solution, and thereafter thelatter separated in the centrifuge.

mixture is subjected to separation such as by the use of a centrifuge.

In another method for the refining of fatty oils with aqueous sodiumcarbonate, the necessity for the use of 1 the aforementioned dehydrationand rehydration steps 1 fatty oils result from:

bran oilitallow, lard, grease, fish oil and whale oil. The 1 (1) Theentrainment of neutral fatty oil in the soapstock formed;

(2) The absorption of neutral fatty oil in the gums which separate alongwith the soapstock;

(3) The saponification of neutral fatty oil into soapstock; and

(4) The emulsification of neutral fatty oil in the soapstock phase.

While by the use of the aforesaid commercial process, these losses ofneutral fatty oil may be very considerably reduced over the losses whichoccur when refining fatty oil by the old batch kettle method employingcaustic soda, i. e., sodium hydroxide as the refining reagent, there isnevertheless considerable room for improvement. Moreover, these priorart methods employing aqueous sodium carbonate as the refiningreagentare complicated in the one case by the necessity of employingdehydrastock containing an excessive amount of neutral oil.

Since, as pointed out above, the amount necessary to neutralize the freefatty acids is very considerably in excess of the theoreticalstoichiometric amount, the amount of sodium carbonate employed in thelatter process when expressed as a multiple of the theoreticalstoichiometric amount is far greater than the numeral three .given as alower limit.

The present invention resides in the discovery that by the employment incombination of (l) relatively high temperatures; (2) relativelyconcentrated aqueous sodium carbonate solutions, and (3) an appropriatestoichiometric relationship between the sodium carbonate contained insaid solutions and the free fatty acid contained in the oil to berefined, not only are the major difliculties inherent in prior processesavoided, permitting manifold simplification of the process steps, butalso the losses are markedly reduced. In addition, when a secondrefining step is employed such as to further reduce color, e. g., by theuse of a wash with aqueous caustic soda as is common in the art, agreater reduction in color of the oil usually can be obtained in suchre-refining when the initial refining is performed in accordance withthis invention, rather than by such prior art processes, particularly inthe case of relatively highly colored oils such as expeller cottonseedoil.

While the practice of the new process, as above defined, results inoutstanding savings in neutral oil over prior art practice, it is foundthat additional savings may be arations of soapstock and oilfromeachother obtained,

by venting off from the mixture of oil and reagent after mixing, butbefore centrifugal separation, at least a portion of any gases,-including carbon dioxide, present: in the vapor phase undertheprevailing conditions.

Further features of the invention will become apparent topersonsskilledin the artas the specification proceeds and upon referenceto the drawings in which:

Figure 1' is a flow diagram ilustrating one adaptation of the invention;

Figure 2 is a-flow diagram illustrating another adaptation'of theinvention; and

Figure 3: is a flow diagram illustrating still another adaptation of theinvention.

In Figure 1 of the drawings at is shown a source of fatty oil to berefined. This fatty oil flows through line 11 to mixer 12 wherein it ismixed'with aqueous sodium carbonate-flowing from source 13. The ratio ofaqueous sodium carbonate to fatty oil fed to mixer 12 is controlled byproportioning pumps 14 and 15, 'or other suitable device or devices.

The mixture of oil and aqueous sodium carbonate flows from mixer 12through heater lfi wherein the temperature of the mixture is raised.After being heated in heater 16 the mixture flows to centrifuge 17wherein soapstock is separated from the oil, the soapstock flowing fromcentrifuge 17 as indicated at 18, and the oil flowing from centrifuge.17 as indicated at 19.

Centrifuge 17 maybe of any desired construction for the separation ofthe phases. It may operate, for example, on the so-called open bowlprinciple, or it may operate on the so-called full bowl principle. As iswell known, the discharge of the separated phases in the caseof an openbowl is over weirs or weir-like devices spaced from the axis ofrotation, the heavier phase being discharged at a greater radialdistance from the axis than the lighter phase. An air core is formed inthe bowl adjacent to the axis of rotation, which preferably is vented,i. e., open to the atmosphere, such as in the case of the centrifugeshown in U. S. Patent 1,634,243, and when so vented, an open bowl isoutstandingly adapted to the practice of the invention.

When operating with a full bowl, on the other hand, the bowl ismaintained completely full of liquid when in operation, and thedischarge of the lighter phase is along the axis of rotation. Sincepressure on the feed to the bowl is required to maintain it full ofliquid, a seal is necessary between the stationary feed pipe and therotating bowl. Also, since it is usually necessary to provide a backpressure in one of the discharging streams to obtain the desiredposition of the interface between the phases in the bowl, it iscustomary to provide a seal between the stationary discharge pipe forthat phase and its outlet on the rotating bowl. Frequently, a seal isalso provided between the stationary discharge pipe for the other phaseand its outlet on the rotating bowl.

The construction and operation of centrifuges of both the open bowl andfull bowl types are well known, and both types are readily available inthe trade.

The mixture of oil and reagent in the practice of the invention isbrought to a temperature of at least 180 F. prior to separation, and isat a temperature of at least 180 F. at the time of separation. Themixture may be heated to the desired temperature in heater 16 orotherwise, e. g., the oil and/ or reagent may be heated in whole or inpart prior to mixing, in the case of the oil preferably not much above110 F. in order to avoid possible fixing of color, particularly in thecase of cottonseed oil.

.Whcn operating with a bowl of the open type, the mixture is usuallyheated to between 180 F. and 212 F-., although higher temperatures maybe employed if desired, such as up to 220 F. or 225 F., particularlywhen pressure is applied during heating. Elevated pressures may beconveniently applied by inserting a constriction in line 20 leading fromheater 16, such as illustrated at 21. The constrictedfeed orificeordinarily employedin feeding a bowl of the open type, and. positioned,for example, at the end of line 20, serves excellently for the purpose.Feed pressures of from 5 to 20 pounds per square inch gauge are commonlyemployed. Any vaporization which might possibly occur upon the releaseof any pressure imposed upon the feed does not interfere with theseparation.

What has. been said with respect to heating the feed mixture whenoperating with a bowl of the open type applies equally whenoperatingwith a bowl'ofthe closed or full bowl type. Since, when operating with aclosed bowl it is possible to apply fairly high elevated pressures tothe mixture being separated, particularly when appropriate backpressures are applied to the respective discharging streams, fairly highrefining temperatures, such as up to 350 F. may be employed. Feedpressures of from 25 to pounds per square inch gauge are illustrative.It is also possibleto operate at similar elevated refining temperaturesand pressures with a conventional open type centrifuge by surroundingthe same with a closed pressure chamber through the walls of which thevarious inlet and outlet conduits extend, and equalizing the pressurebetween the closed chamber and closed receiving tanks such as the tanks22 and 22'a in which the separated materials are collected. Appliedpressures are, of course, toavoid undue vaporization at. the elevatedtemperatures employed, such as of the water present.

' Any desired contact time between oil and reagent may be employed, suchas between one minute and thirty minutes, lower contact times beingpreferred.

The concentration of the aqueous sodium carbonate fed to mixer 12 is atleast 22 B. It is found that a good working range is between 22 B; and30 B. although aqueous sodium carbonate solutions of higher Baum may beemployed, particularly if the. aqueous sodium carbonate is maintained atelevated temperaturev at its source to avoid precipitation of solidsodium carbonate therefrom which preferably is avoided.

Whereas in prior processes for the refining of fatty oils with aqueoussodium carbonate, a multiple of the amount necessary to neutralize thefree fatty acidspresent in the oil is employed as the criterion inarriving at the amount of alkaline agent to be employed, it has beendiscovered that in the practice of the present invention the percentageof free fatty acids in the oil is of major importance, and

. that such percentage is of necessity the criterion in arriving at anappropriate ratio of reagent to oil to be employed to obtainoutstandingly low losses. In the practice of the present invention theamount of sodium carbonate employed forrefining is from 2 to 3 times thetheoretical stoichiometric amount for the particular oil being refined,free fatty acids being calculated as oleic acid in accordance with Wellestablished custom in the trade.

Thus if a fatty oil shows a free fatty acid content of 1% by weight, onewould employ between 0.38% and 0.57% by weight based on the oil ofsodium carbonate on a dry basis in an aqueous solution of at least 22 B.For best results the soapstock at the temperature at which it isseparated should be free-flowing. Appropriate conditions of fluidity areinherent in the practice of the new process.

The centrifugal force employed. in the separation of soapstock from therefined oil is preferably at least 5000 times gravity determined at theinner periphery of the bowl at its greatest inner radius, andparticularly 8000 times gravity and above. Outstanding results areobtained when the foregoing centrifugal force is at least 10,000 timesgravity.

, As indicated above it is common practice, particularly with highlycoloredoils, to subject the same to a second refining treatmengcommonlywith caustic soda, primarily for the purpose of further reduction incolor, and fre quently accompanied by some further reduction in freefatty acid content.

Returning now to Figure 1 of the drawings, as shown, the refined oilleaving centrifuge 17 through line 19 is delivered to a container 22.For rerefining purposes, as illustrated, the refined oil is pumped fromcontainer 22 by pump 23 through cooler 24 wherein the temperature of theoil preferably is reduced for example to 100 F. or below. The purpose ofcooling the oil at this point is to avoid contacting the oil'withaqueous caustic soda at a relatively high temperature, which appears atleast in some cases to fix color in theoil beyond removal. If fixing ofcolor due to temperature does not present a problem, the cooling stepmay be avoided.

From cooler 24 the oil flows to mixer 25 through line 26 wherein it ismixed with aqueous caustic soda pumped from source 27 by means ofproportioning pump 28. The mixture flows from mixer 25 through heater 29wherein the temperature of the mixture is raised to say between 120 F.and 160 F., whereupon the mixture is delivered to centrifuge 30 for theseparation of the oil from the reagent phase. As shown the oil flowsfrom centrifuge 30 through line 33, and the reagent through line 34. Theuse of from 1% to by weight based on the, oil of aqueous caustic sodasolution of from 8 to30 B. is typical of usual operations. Any otherrerefining procedure may be employed.

. Aspointed out above, the initial refining of the oil by the use ofthis invention assists in obtaining an oil of lower finished color uponrerefining, then when prior art processes are employed for such initialrefining.

Also as pointed out above, additional savings in neutral oil mayfrequently beeffected, and even better centrifugal separationsofsoapstock and oil from each other obtained, by venting off from themixture of oil. and reagent, after mixing but before centrifugation, atleast a portion of any gaseous material that might be present. One meansofaccomplishing thispurpose is illustrated in Figure 2 wherein themixture of oil and reagent leaving heater 16 is conducted to container40 having a vent 41 at the top thereof. Vent 41 may be. of any desired.construction capable of permitting passage therethrough of gases 'whilepreventing the passage of liquid, manydifferenttypes of which are wellknown in the art. .A typical gas vent valve is illustrated as comprising,a float 42 to the upper portion of which is attachedaivalve stem 43held in sliding position by a guide 44, and the upper end of whichengages a valve seat 45 to close the opening therein when the float 42is moved upwardly due to the entry of liquid into thevent 41. Movementof float 42 downward due to the accumulationof gas invent 41 causes thevalve to open to permitthe escape of gas. Any other suitable device maybe substituted.

The mixture of oil and reagent is fed through heater 16 and throughcontainer40, e. g., under the pressure supplied by pumps 14 and 15 (seeFigure 1), tending to keep the container 40 full of liquid in view ofthe operation of the vent 41. From' container 40 the mixture flows tocentrifuge 17, e. g.,. through line 47.

It will be appreciated that the mixture flowing through container 40 maybe under any desired elevated pressure, and that the vent 41 willnevertheless functionfor the venting off of gases. s I g A simplerarrangement for the venting oif of gases from the mixture of oil andreagent is illustrated in Figure 3 wherein the flow from heater 16 isinto a container 50 having a simple vent 51 to the atmosphere.

When employing a simple vent, such as 51, it is preferred to control theamount of liquid mixture in container 50. This may be done, for example,by means of a-float controlled valve 52 in exit line 59, and operated.by float mechanism 53 comprisingfloat 54, lever arm 55 and links 56 and57. Pump 58 pumps the mixture through the valve 52, and the rate of flowthrough the valve 52 is controlled by the vertical position of float 54,valve 52 being moved toward open position upon rise of the float 54 andmoved toward closed position upon lower-.

stood that, broadlyspeaking, the vent may be positioned at any desiredpoint between the mixing and the centrifuging, also a plurality of ventsmay be employed, e. g., for the venting of gases both upstream anddownstream of the heater 1 6.

In the industry itis customary to subject the refined oil, or, if rerefining is resorted to, the rerefined oil, to

water washing to remove any possible residual soapstock and/ or reagent.This is followed by drying of the oil, customarily under vacuum. i I lThe following examples of the practice of the invention are given byway' of illustration and not of limitation.

. Example 1, Q Corn oil having a free fatty 'acid content of 2.0% wasrefined under temperature conditions'between 185 F. and 205 F. withanaqueous sodium carbonate solution of 22 B. Four different continuousruns were made in which theamount of sodium carbonate based on thetheoretical stoichiometric amount was as follows: Run No. 1.1.7 timesthe theoretical stoichiometric amount.

Run N0. 2.2.8 times the theoretical stoichiometric amount. v

Run No. 3.-3.5 times the theoretical stoichiometric amount. I a Run No.4.6.1 times the theoretical stoichiometric amount. j

After centrifugal separation of the soapstock from the refined oil ineach case, the oil was continuously rerefined under temperatureconditions between 140 F. and 150 F. with 1.5 by weight based on the oilof aqueous caustic soda solution 015 20" B. This was followed in eachinstance with centrifugal separation of the regeant from the oil, andthen by conventional water washing of the oil with subsequent dryingthereof under vacuum. The results were as follows:

Run No.: Percent Refining Loss Example ii Corn oil having a free fattyacidcontent of 1.2% was stream with 1.5% by weight based on the oil ofaqueous caustic soda solution of 20 B.iunder temperature conditions,between F. and .F. Upon separation of the reagent from the oil bycentrifuging, the oil upon analysis showed a free fatty acid content of0.04%. The oil was then water washed and vacuum "dried in a,

conventional manner. The overall loss was 2.85% by weightbased'ontheoriginal oil. The refining loss as determinedanalytically, employing theapplicable official method ofthe American Oil Chemists Society, was

' 'Corn'oilhavi'ng a: free fattyacid content of- 2.1% by weight wasrefined in a continuous'stream under temperature conditions between 200F. and 205 F. with an: aqueous: sodium carbonate-solution of 22 B., theamount of sodium carbonateemployed being 2.5 times the theoreticalstoichiometric amount. After separation of the soapstock from the oilbycentrifuging, the

Examplev 4 l2 tank cars of a highly colored cottonseed oil having anaverage free fatty acid content of 1.6% by weight was refined in acontinuous vented stream under temperature conditions between 200 F. and210 F. with an aqueous sodium carbonate solution of 26" B. The amount ofsodium carbonate employed was between 2 and 3 times the theoreticalstoichiometric amount, the average being 2.1 times. After separation ofthe soapstock' from the oil by centrifuging, the oil upon analysisshowed an average free fatty acid content of 0.06%. The separated oilwas rerefined in a continuous stream under temperature conditionsbetween 155- F. and 160 F. with 3% by weight based on the oil of. anaqueous caustic soda solution of 20 Be. After separation of the reagentfrom the oil by centrifuging, the oil upon analysis showed an averagefree fatty acid content of .02%. The oil was then subjected toconventional water washing and vacuum drying. The overall loss was 6.1%by weight based on the original oil, and the final refined oil had anaverage bleach color of 20 yellow, and 2.4 red, which is an outstandingresult since it exemplifies the refining of highly coloredcottonseed oilinto what is known in the trade as a prime oil, i. e., an oil having ableach color not greater than'2.5 red, which is an extremely difiiculttask as exemplified by the color obtained through laboratory refining asnoted below. The average laboratory refining loss as determinedanalytically, employing the applicable official method of the AmericanOil Chemists Society, was 8.1% by weight, and the average bleach colorso determined was 20 yellow and 2.7 red. The outstanding resultsobtained are pointed upby the fact that it is extremely difficult in thecase of a highlycolored cottonseed oil to reduce the red bleach colorbelow that obtained by the above ofiicial method.

Any other fatty oil may be substituted in the above examples withcomparable results. Likewise any other temperature conditions, any otherratio of sodium carbonate to free fatty acids, any other concentrationof sodium carbonate in aqueous solution, any other ratio of caustic sodato oil for rerefining, any other concentration of caustic soda inaqueous solution for refining, etc., as set forth herein and in theclaims, may be substituted in the above examples with comparableresults.

While the centrifugal'forces used in the separations effected in theforegoing examples were between approximately 10,000 and 15,000 timesgravity, lower centrifugal forces may be substituted in these exampleswith the unexpected results to which this invention relates.Alsofull'bowl separation may be substituted for the open bowl separationemployed in the examples, although the open bowl; separation with theatmospheric venting employed is preferred; Likewise, separation bygravity may be substituted, but with less efficient-separation.

For purposes of simplicity and convenience-in description, auxiliaryequipment such as pumps, valves, motors, controls, thermometers,pressure gauges, strainers, flow meters andthe like, have been omittedfrom the flow diagrams, since these items and their use in awelldesigned plantiwill immediately occur to the skilled engineer uponbecoming familiar herewith.

While specific conditions for the refining of fatty oils have beendescribed, it is to be understood that this is by way of illustration,and that modifications may be made without departing from the spirit ofthe invention. Accordingly it is intended that the patent shall cover,by suitable expression in the claims, the various. features ofpatentable novelty that reside in the invention.

We claim:

'1. A process for the refining of a fatty oil containing free fatty acidwhich comprises combining a stream of said oil and a stream of aqueoussodium carbonate solution of at least 22 B. in measured quantity suchthat the amount based on the free fatty acids contained in said oil ofsodium carbonate added to said oil is from 2 to 3 times the theoreticalstoichiometric amount for said oil, venting gas from said combinedstreams of oil and aqueous sodium carbonate solution, thereafter andwhile in mixed state flowing said combined streams at a temperature ofat least F. to a centrifugal separator, and separating in saidcentrifugal separator said oil from the soapstock formed as a result ofsaid treatment.

2. A process for the refining of a fatty oil containing free fatty acidwhich comprises flowing proportional quantitles of said oil and of anaqueous sodium carbonate solution of at least 22 B. into confluence andthen concurrently in a liquid stream and under temperature conditionsbetween approximately 180 F. and 225 F. and with a removal of gastherefrom to a centrifugal separator, and separating the oil from thereagent phase in said centrifugal separator, the amount based on thefree fatty acids contained in said oil of sodium carbonate added to;said oil being from 2 to 3 times the theoretical stoichiometric amountfor said oil.

3. The process of claim 2 in which the temperature conditions referredto are maintained between approximately 180 F. and 212 F.

4.' The process of claim 2 wherein the separation takes place in acentrifugal separator having a bowl of the open type.

5. The process of claim 4 wherein the bowl is vented to the atmosphere.

6. The process of claim 2 wherein separation takes place undercentrifugal forces of at least 5000 times a ty- 7 7. The process ofclaim 6 wherein separation takes place' under a centrifugal force of atleast 8000 times gravity.

8. The process of claim 7 wherein separation takes place under acentrifugal force of at least 10,000 times gravity.

' 9. The process of claim 2 wherein the final separated oil is rerefinedwith caustic soda to reduce color in the oil.

10. The process of claim 9 wherein the oil is a vegetable oil. p

11. The process of-claim 10 wherein the oil is cottonseed oil.

12.; The process of claim 2 wherein the aqueous sodium carbonatesolution employed is between 22 B. and 30 B.

13. The process of claim 1 in which the venting of gas from the combinedstreams of oil and aqueous sodium carbonate solution takes place afterheating but before centrifuging.

14. A process for refining a fatty oil containing free fatty acid whichcomprises combining a stream of said oil and a stream of aqueous sodiumcarbonate solution of between 22 B. and 30 B. in measured quantity suchthat the amount of'sodium carbonate combined with said oil is from 2 to3 times the theoretical stoichiometric amount for neutralizing the freefatty acid contained in said oil, maintaining said combined stream underpressure conditions of at least 5 pounds per square inch, heating saidcombined stream to within a temperature range of from 180 F. to 212 F.,venting gas from said combined stream while still under theabove-mentioned temperature and pressure conditions, thereafterintroducing said combined stream while still under the above-mentionedtemperature conditions into a centrifugal separator 15 2607788 10operating on the open bowl principle with the bowl vented to theatmosphere, and separating in said centrifugal separator under acentrifugal force of at least 10,000 times gravity said oil from therest of said combined stream including the soapstock formed as a resultof said treatment.

References Cited in the file of this patent UNITED STATES PATENTS2,190,594 Clayton Feb. 13, 1940 2,245,846 Ayres June 17, 1941 2,349,701Clayton July 15, 1941 2,249,702 Clayton July 15, 1951 Clayton Aug. 19,1952

1. A PROCESS FOR THE REFINING OF A FATTY OIL CONTAINING FREE FATTY ACIDWHICH COMPRISES COMBINING A STREAM OF SAID OIL AND A STREAM OF AQUEOUSSODIUM CARBONATE SOLUTION OF AT LEAST 22* BE. IN MEASURED QUANTITY SUCHTHAT THE AMOUNT BASED ON THE FREE FATTY ACIDS CONTAINED IN SAID OIL OFSODIUM CARBONATE ADDED TO SAID OIL IS FROM 2 TO 3 TIMES THE THEORETICALSTOICHIOMETRIC AMOUNT FOR SAID OIL, VENTING GAS FROM SAID COMBINEDSTREAMS OF OIL AND AQUEOUS SODIUM CARBONATE SOLUTION, THEREAFTER ANDWHILE IN MIXED STATE FLOWING SAID COMBINED STREAMS AT A TEMPERATURE OFAT LEAST 180*F. TO A CENTRIGUGAL SEPARATOR, AND SEPARATING IN SAIDCENTRIFUGAL SEPARATOR SAID OIL FROM THE SOAPSTOCK FORMED AS A RESULT OFSAID TREATMENT.